1. Field of the Invention
The present invention relates to a thin-film-transistor liquid-crystal display (TFT-LCD), and more particularly, to a TFT-LCD with a high aperture ratio and with a reduced coupling effect.
2. Description of the Prior Art
Within the popularity of LCDs, display devices from small size to large size usually include TFT-LCDs. However, because the TFT-LCD with smaller size has a smaller displaying region, an aperture ratio of the TFT-LCD with smaller size is lower than the TFT-LCD with larger size in the same resolution so that brightness and contrast of the TFT-LCD with smaller size are reduced. Besides, when the TFT-LCD with a higher resolution is required, the aperture ratio of the TFT-LCD with a higher resolution will also be reduced. Therefore, in order to maintain high brightness in a display, brightness of the backlight should be increased, but cost of the backlight module will be also increased. How to increase the aperture ratio is therefore an important aspect in developing the TFT-LCD.
In the prior art, a poly-silicon TFT-LCD has been already developed. The electron mobility of the poly-silicon is about ten to hundred times higher than the electron mobility of the normally used amorphous silicon, so that the size of the TFT can be reduced so as to have a higher aperture ratio. However, manufacturing methods of the poly-silicon TFT require a manufacturing temperature higher than a temperature of manufacturing an amorphous silicon TFT, and the manufacturing methods of the poly-silicon TFT also require a laser annealing process for transforming the amorphous silicon structure into the poly-silicon structure. Therefore, in the field of cost and yield, the manufacturing methods of the poly-silicon TFT-LCD are not as good as the manufacturing method of the amorphous silicon TFT-LCD.
Referring to FIG. 1 and FIG. 2, FIG. 1 is a schematic diagram illustrating a top view of a pixel structure of TFT-LCD according to a prior art, and FIG. 2 is a schematic diagram illustrating a cross-section along line AA′ of FIG. 1. As shown in FIG. 1, a pixel structure 10 of the TFT-LCD includes two scan lines 12 parallel to each other, two data lines 14 perpendicular to the scan lines 12, a TFT 16 disposed at a border between the data line 14 and the scan line 12, a common line 18 disposed between the scan lines 12, and a pixel electrode 20 overlapping a part of the scan lines 12 and the data lines 14, wherein the TFT 16 includes a source electrode 110 and a drain electrode 120. Because the pixel electrode 20 overlaps the scan lines 12 and the data lines 14, coupling capacitances between the pixel electrode 20 and the scan lines 12 are generated, and coupling capacitances between the pixel electrode 20 and the data lines 14 are also generated.
As shown in FIG. 2, the pixel structure 10 further includes an array substrate 22, an organic layer 24, a conductive layer 26, a gate insulating layer 28, and a passivation layer 30. The TFT 16 and the common line 18 are disposed on the array substrate 22. The conductive layer 26 disposed between the gate insulating layer 28 and the passivation layer 30. The organic layer 24 is disposed between the passivation layer 30 and the pixel electrode 20, and the organic layer 24 and the passivation layer 30 both have two through holes 32, 34, so that the pixel electrode 20 can be electrically connected to the drain electrode 110 via the through hole 34 and connected to the conductive layer 26 via the through hole 32. The prior art provides the organic layer 24 and increases the thickness of the organic layer 24 so as to reduce the coupling capacitances between the pixel electrode 20 and the scan lines 12 and the data lines 14, and then, the coupling effect can be reduced. However, in the prior art, the organic layer 24 between the pixel electrode 20 and the passivation layer 30 should also be provided, and the organic layer 24 should have a thickness about 3 micrometers. This means that the manufacturing cost will be increased, and the thickness of the pixel structure 10 of TFT-LCD will also be increased. Therefore, to raise the aperture ratio without increasing manufacturing cost and with reduced coupling effect is an extremely important goal.